Linevyvh Y. One-dimensional silicon nanostructures for physical and chemical sensors

The work is devoted to the study of an array of silicon nanowires (SiNWs) and its modifications for use in sensors of physical and chemical quantities. The scientific and applied research presented in this thesis focuses on the practical study of the influence of technological parameters of SiNWs array creation on the static and dynamic parameters of sensors based on it. Nanoscale silicon one-dimensional structures are becoming increasingly common in modern scientific and technical research into physical and chemical sensors. They have unique properties, such as high aspect ratio and large specific surface area, which can significantly increase the sensitivity of sensors. One-dimensional structures made from silicon are used in various fields, including medicine, environmental monitoring, food industry, and everyday life. Their use makes it possible to create highly sensitive sensors for measuring of temperature, light, humidity, and detecting of various gases and chemicals (VOCs). Silicon nanowires, which are the basis of such sensors, can be fabricated using various methods, including chemical vapor deposition (CVD), chemical etching (MACE), and lithography. In this work, we investigate the properties of SiNWs obtained using the MACE method. In particular, a comparative analysis of the effect of various technological parameters of SiNWs synthesis (duration of the first and second stages of MACE, as well as the content of solutions) and the type of modification on the static and dynamic parameters of sensors to various physical and chemical quantities was carried out. The relevance and novelty of the dissertation research is due to the need to determine the optimal parameters for the synthesis of silicon 1D structures to create various sensors of physical and chemical quantities, as well as to improve stability, sensitivity, performance and selectivity by means of their surface modification. In the first chapter, we investigated the technologies, materials, and designs of sensors based on nanoscale silicon 1D structures for sensing chemical and physical quantities. It was found that sensors based on SiNWs have high sensitivity and adsorption properties due to their unique electronic properties and developed surface structure, which ensures accurate detection of various chemical and biological compounds. Other advantages of SiNW-based sensors include room temperature operation and compatibility with ICs, and due to their miniature size, these sensors can be used in various fields, including air and water pollutant monitoring and medical diagnostics. However, a review of the literature revealed several major problems with such sensors. First, SiNW-based sensors often have limited stability under different operating conditions, which can affect the accuracy of measurements. Secondly, such devices are characterized by relatively long response and recovery times, which determine the low speed of the sensor. Third, the durability of such sensors requires additional research, as silicon tends to oxidize over time. To overcome these problems, this paper proposes several promising approaches: improvement of the technological parameters of SiNWs array synthesis and the use of various types of their surface modification, which can improve the performance, stability, and sensitivity of such sensors. In the second chapter, it was described the fabrication of sensitive structures based on an array of SiNWs for physical and chemical sensors with planar contact geometry (resistive/capacitive type) and showed the effect of SiNWs fabrication parameters on their surface morphology, as well as static parameters (response and sensitivity) and dynamic parameters (response time and recovery time) of sensors based on them. It has been shown that the addition of one-dimensional silicon nanostructures to the composition of physical quantity sensors has significantly improved their sensitivity and performance. In particular, it was found that an increase in the resistivity of the device substrate leads to a significant deterioration in the response for temperature and light sensors, but to an improvement in humidity and VOC sensors. Additional treatment before the MACE operation (texturing) improved the response for light sensors, but worsened the response for temperature, humidity, and VOC sensors. Increasing the time of AgNPs deposition resulted in a deterioration of the response for all sensors. A significant increase in the time of silicon etching leads to a deterioration in the response of temperat